Structural and nanoacoustic characterization of Co/Pt ferromagnetic superlattices

Abstract

Superlattices (SLs) with spatially modulated elastic properties-particularly those based on III–Vsemiconductors-have emerged as key platforms for reaching the ultrahigh-frequency(GHz–THz) regime in nanoacoustic devices. The exploration of alternative materials withmultifunctional properties remains a rich and promising area of research. In this work, weinvestigate the structural, magnetic, and acoustic properties of nanometric Co/Pt SLs. X-rayreflectometry reveals a well-defined periodicity, while scanning transmission electronmicroscopy combined with local compositional analysis shows that the SLs exhibit acompositional modulation rather than sharp interfaces. The polycrystalline nature of thestructures is confirmed by both x-ray diffraction and transmission electron microscopy.Magnetization measurements indicate the presence of perpendicular magnetic anisotropy athigher Co concentrations. Picosecond acoustic experiments demonstrate that the SLs supportshort-lived acoustic modes up to 900 GHz, along with up to seven acoustic echoes withfrequencies ranging from 40 to 250 GHz. These findings open a path toward investigatingphonon-driven magnetization dynamics in such structures, establishing a foundational step toward the development of magnetoacoustic devices operating at ultrahigh frequencies.